Adsorption and surface dilational visco-elasticity of CnEOm solutions as studied by drop profile analysis tensiometry

Abstract

The surface tension isotherms and dilational visco-elasticity for three nonionic surfactants (C10EO8, C12EO5 and C14EO8) were comparatively studied using the bubble and drop profile analysis tensiometry. The experiments based on drop profiles were analysed assuming the depletion of surfactant molecules from the bulk of the drop due to adsorption. To process the experimental results, two theoretical adsorption layer models (Frumkin and reorientation) were applied, while the reorientation model provides a better description of the experimental results. In addition, the visco-elasticity moduli obtained from drop and bubble profile experiments were compared. It was shown that at higher surfactant concentrations the drop profile method provides visco-elasticities systematically larger than those obtained from bubble profile experiments, even though the adsorption-related depletion has been correctly considered. The proposed correction protocol provides the option for direct comparison between data obtained by the drop profile analysis method with those from other methods.